wireprotov2: handle noop action

This action can be returned from the client reactor. We should
handle it.

Differential Revision: https://phab.mercurial-scm.org/D4923

mercurial/wireprotov2peer.py

@@ -325,6 +325,8 b' class clienthandler(object):'
                 raise e
 
             return
+        elif action == 'noop':
+            return
 
         if frame.requestid not in self._requests:
             raise error.ProgrammingError(